Following this guideI try to enable varnish to handle HTTPS request.I'm not able to get works Varnish and I get 503 error.Forget to mention that Magento is installed on Google Compute EngineCould you help me please?Regards

Here we have the required step in order to get Varnish working with our Magento stack. Could you please try to follow it. Please before, revert the changes you did and that are you causing the 503 error. If you cannot do this could you provide us with the following log files?

If you want to use Varnish with HTTPS there is a bad new. Varnish does not support HTTPS requests. In order to mitigate it, there are some typical configuration scenarios that you can try.

They consist of using a scenario where you have two web servers and varnish acting in between them. Our Magento stack has the part of this topology closer to the application. Then you need to set up a new server that handles HTTP and HTTPS request, it redirects the petitions via HTTP to varnish and the classsic web server.

In order to understand better what I suggest there are some links detailing this solution:linode.com

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